Based on the average values, am I correct in assuming that I have relatively soft water? Should I concern myself with additions to make my water harder, if I am making porter by steeping specialty grains and using an extract?

I didn't want to overreach as I'm very much a newbie on this forum. Basically what I'm trying to understand if what, if anything, I should do to my water if I am brewing by steeping special grains and then using an extract.

In terms of taste, the tap water out here in Long Island has always tasted kind of bland, which is I guess a reflection that there do not seem to be a lot of salts and minerals in it. Bland may be not such a bad thing, I guess, if you can tweak the profile a bit to match a style of beer. On the other hand, several threads on this forum have suggested that extract brewers shouldn't worry too much about water profiles, unless your water is very hard or tastes bad.

My lhbs guy said that I might consider adding some gypsum and non-iodized salt if I wanted to brew some porter next week, but how much?

This is a great forum, by the way. I have gone from using a simple beer kit to using basic but important additions for what will be my second beer, namely:

better sanitation
full boil system
primary fermenter with temperature control
kegging

Understand also that I am not interested in merely duplicating a London profile, for example, since I don't know what London porter brewers do to their beer. A simple way of getting my local water to be more amenable to a Porter style is all that I'm after.

Honestly I wouldn't do anything with your water for extract brewing, except maybe a tsp or so of gypsum per 5 gallons on hoppy beers where you want to accentuate the bitterness. If you get into all grain you may need to make some more additions but that's pretty nice water to start with. Alkalinity is the other thing you'll want to know for all grain, and yours is relatively low at 35 avg.

That's kinda what I was thinking as several threads suggest that since you don't know how the extract effects the water profile, you're rolling the dice if you add a lot of minerals to water that's already good. All I really have to do, honestly, is leave my water out over night to get rid of the chlorine. I was also thinking about getting a profile from the wort from Wards, but seriously, if I'm willing to do that then it makes more sense to engineer from the front-end with all-grain than to try to reverse-engineer from the back end.

That's kinda what I was thinking as several threads suggest that since you don't know how the extract effects the water profile, you're rolling the dice if you add a lot of minerals to water that's already good. All I really have to do, honestly, is leave my water out over night to get rid of the chlorine. I was also thinking about getting a profile from the wort from Wards, but seriously, if I'm willing to do that then it makes more sense to engineer from the front-end with all-grain than to try to reverse-engineer from the back end.

Those are chlorides, and they're not going to come out ... But don't worry about it. Unless there is a strong chlorine scent, it's probably fine. If there IS. A strong chlorine scent, chances are your water district uses chloramines, as they're more stable. Best way to get rid of those is with a Camden tablet.